A lorry transporting an excavator has overturned on the M6, forcing police to close all southbound lanes near Preston.
The lorry jackknifed before overturning near junction 31a at around 9.10am, spilling around 200 litres of fuel across the carriageway.
Police said the leaked diesel has spread over all lanes for at least half a mile.
Highways have now completely closed the M6 southbound between junction 32 (Broughton, A6, Blackpool, M55) and 31a (Preston, Longridge).
Police and Highways are warning that the motorway is expected to remain closed into the afternoon.
Miles of trapped traffic is using the hard shoulder to pass the scene under the management of traffic officers.
A police spokesman said: "The motorway is now closed southbound between junctions 32 and 31A and is expected to remain closed for some time.
"There is a large quantity of diesel spilled on the carriageway and this needs to be cleaned up for the safety of all motorists, which is of course our priority.
"We are in the process of diverting those stuck on the M6 off the motorway but this could take some time.
"We are advising all motorists to avoid the area and find alternative routes where possible."
A Highways spokesman added: "The M6 is currently closed due to a lorry carrying plant machinery which has overturned causing significant damage and spillages of fuel.
"Due to the location of the incident the M55 eastbound link to the M6 south is also closed.
"There are long delays approaching both the M6 and M55 closures.
"Traffic officers are on scene and resources are being arranged to recover the involved vehicles and clear the carriageway."
Eyewitnesses said the large excavator fell from the lorry after it jackknifed, blocking three lanes of the busy carriageway.
North West Ambulance Service attended and treated a man who is described as 'walking wounded'.
Highways said the 4-mile stretch of motorway is expected to remain closed until around 12.30pm.
Diversions are signed by the solid square diversion symbol and are as follows:
- Exit M6 J32, Blackpool, onto M55. Exit M55 J1, Broughton, take first roundabout exit, A6 Preston.
- At the A6/A5085 junction turn left (M6 South).
- Follow the A5085 to the A59 roundabout.
- Take the first exit and follow the A59 to M6 J31, Tickle Trout.
- At the first roundabout take the second exit, M6 South, Birmingham.
- At the second roundabout take the second exit to rejoin the M6 southbound.
- For traffic approaching the delays locally, you are advised to expect disruption with extra journey time and you may wish to re-route or delay your journey.
If travelling towards this area from much farther afield, delay information will remain visible on our on-road variable message signs until delays have cleared.